1. Field of the Invention
The present invention relates to a power supply capable of selecting an independent overload protection circuit or a group overload protection circuit for a plurality of loads that require a large electric power output, such that users can select the appropriate electric power output according to the capacity requirement of the loads.
2. Description of the Related Art
Science and technologies advance rapidly, and electronic technology is well developed. Computer systems become increasingly more powerful as the functions of central processing units (CPU) and graphic cards are enhanced. With a variety of other additional functions, the functions of component modules that constitute the basic architecture of a computer become more powerful accordingly and maximize the utility of the whole system. For instance, the specifications of central processing units are improved from single-core to dual-core architecture, and the graphic cards are upgraded to the high-resolution 3D effect for high-level computer players, and some computer systems even employ more than two or three graphic cards.
At present, a high-end graphic card requires an electric power of 150 watts, and a set of computer system consumes an electric power of 300˜450 watts for its graphic cards, and thus the past power supply of 300˜350 watts no longer can meet the requirement now. Furthermore, the quantity of other hard disk drives, optical disk drives and USB connectors increases and each device requires a lower voltage (in volts) and a higher electric power (in watts), so that the system can maximize its utility, and the design of power supply tends to be high power.
Since it is necessary to take the user's safety into consideration for the design of the power supply, the SSI and UL specifications sets a critical value for the maximum output power of a single load. For example, the SSI 1 specification sets the critical value to 240 VA, which means that a current has an upper limit of 20 amperes (A) when the output voltage is 12 volts (V). The upper limit of the current is set to 20 amperes (A) for protecting the safety of computer users. However, a professional user generally connects many peripherals to the computer system, and thus a higher electric power is required. To meet this requirement, power supply manufacturers generally design and develop a power supply system with high power. As a result, a higher development cost is incurred. Furthermore, the power supplies come with various different specifications, and thus both manufacturing and carrying costs are increased as well.
In view of the foregoing shortcomings of the prior art, some designers proposed a power supply that allows users to select or increase the output power, and such power supply combines a plurality of power supplies to increase the total output power. For example, the original output current of a load is 20 A, and a select circuit is provided for users to set the output load to 30 A or above. Although this method can increase the output power of the load, the protection circuit is triggered to disconnect the power when the output power of a load is higher than the maximum allowed output power such as an output over 30 A, and the current requirement of other loads is lower than 20 A, and the sum of two output power is smaller than 50 A, and thus this method is very inconvenient and not suitable for practical applications.